1. Field of the Invention
The present invention relates to a co-generation system, and in particular, to a hot water supply system utilizing exhaust gas of an engine.
2. Description of the Prior Art
Recently, a co-generation system has been used in which electric power is generated by using a driving force of an engine including a gas engine, diesel engine, gas turbine, or the like, and at the same time, hot water produced by utilizing the exhaust gas of the engine is supplied to a user.
A prior art co-generation system comprises, as shown in FIG. 1, an engine 1, for example, a gas engine having a circulating path 1a for cooling water, a branch circulating path 1b, and an exhaust pipe 1c, an A.C. generator 2, a cooling water heat exchanger 3, and an exhaust gas exchanger 4. The exhaust gas heat exchanger 4 has an exhaust pipe 5 for exhaust gas, and a feed hot water pipe 6.
In the arrangement described above, the A.C. generator 2 is driven by the gas engine 1 and generates electric power, and at the same time, warm water produced as a result of cooling a high temperature portion of the engine 1 is used to warm city water in the cooling water heat exchanger 3 to produce warm water. The warm water is further supplied to the exhaust gas heat exchanger 4 to heat by the exhaust gas supplied through the exhaust pipe 1c thereby to use hot water produced therein as a hot water supply source.
Furthermore, another prior art hot water supply system is shown in FIG. 2, in which as compared with the prior art system in FIG. 1, a warm water heat exchanger 7 and a warm water pump 8 are added to enable to supply potable warm water.
In this system, warm water produced by cooling a high temperature portion of an engine 1 is utilized to warm city water in a cooling water heat exchanger 3, and the warm water produced in the exchanger 3 is further supplied to an exhaust gas heat exchanger 4 to heat the warm water by exhaust gas supplied through an exhaust pipe 1c to produce hot water. The hot water is supplied to the warm water heat exchanger 7 and used as a heat source to heat city water to produce potable hot water for hot water supply to a user.
In this case, the warm water in the primary side of the warm water heat exchanger 7 after being used as the beat source In the warm water heat exchanger 7 is supplied to the cooling water heat exchanger 3 through a warm water pump 8 to utilize again as feed water to the cooling water heat exchanger 3.
In the prior art system described above, as a means for recovering heat from the exhaust gas containing a great amount of heat generated by the engine 1, the exhaust gas heat exchanger 4 which is a heat exchanger of a gas/water indirect type has been used primarily.
As a result, when the heat recovery is to be performed by directly supplying feed water of 20.degree. C. to the exhaust gas heat exchanger 4, the exhaust pipe 5 of the heat exchanger 4 will be corroded at low temperature due to dropwise condensation or sweating caused by a large temperature difference. Accordingly, to avoid this, the feed water is preheated in the cooling water heat exchanger 3 up to about 50.degree. C., and furthermore, the preheated feed water is heated in the exhaust gas heat exchanger 4 to produce hot water of 80.degree. C. to be used as the hot water supply in the system in FIG. 1. On the other hand, in the system in FIG. 2, the hot water produced in the exhaust gas heat exchanger 4 is used as the heat source for the warm water heat exchanger 7 to produce the potable hot water of 80.degree. C. to be supplied to the user.
In the prior art systems, since the exchange system of the gas/water indirect type is employed, evaporation latent heat in the great amount of heat of the exhaust gas can not be recovered, and it is exhausted as water vapour, carbonic acid gas, etc. Moreover, the temperature of the exhaust gas to be discharged is limited to a temperature of 150.degree.-200 .degree. C. in order to prevent the low temperature corrosion. Consequently, the heat efficiency of the overall system has been limited to about 80% even at the maximum.
Furthermore, in the indirect system, since a heat transfer area of the heat exchanger becomes large when a temperature of the gas approaches a temperature of the water, the indirect system is not practical.
Moreover, in the prior art systems, a problem is involved in that it has been impossible to decrease the output or engine speed of the engine when it is required to maintain the amount of heat of the hot water to be supplied at constant, even when small electrical power of the generator is demanded, or the engine speed is permitted to be decreased in relation to the load. Thus, the balancing between the electrical power demanded to the generator and the heat energy required for the heat exchanger is difficult. As a countermeasure to such a problem, an auxiliary boiler has been used to compensate for a decrease of the amount of heat due to a decrease in the output or speed of the engine. However, since the auxiliary boiler is needed additionaly, the overall system becomes large, and the installation are is also increased.
In addition, in the prior art systems, since the warm water heat exchanger is installed in the path before the hot water supply source to the user in order to produce potable hot water, additional piping for this purpose is needed and additional installation area is needed.